Light emitting diode (LED) lamps have unit-to-unit variation in light output characteristics (e.g., color consistency, color stability, lumen stability, etc.) due to material and process variations that affect the production yield. Variations between LED lamps can be due to material characteristics varying across the LED wafer, and process control variations occurring during production. Conventionally, LED lamps are sampled post-production and assigned into performance groups (i.e., ‘binned’) for brightness (luminous flux) and color parameters (chromaticity, temperature, rendering, stability, etc.). LED lamps within the same bin are typically packaged and sold together to maintain the appearance of a consistent product.
LEDs that emit white light can be produced either by mixing the output of red, green and blue (RGB) LEDs to form the white light, or by using a phosphor material to alter the light from a monochromatic blue, or ultraviolet (UV) LED. For example, two complementary colors can combine to form white light. However, the white light formed by these approaches can still have varying spectra, which can cause the color appearance of illuminated objects to vary.
Phosphor-based white LEDs involve coating mostly blue LEDs with different color phosphors (depending on the original LED color). These phosphor-based LEDs have efficiency losses from heat loss and other phosphor-related degradation. Some phosphor-based white LEDs encapsulate InGaN blue LEDs inside phosphor-coated epoxy. A blue-shifted yellow, yttrium aluminum garnet (BSYAG) (BSY/mint/off-state white) LED combined with a red/amber LED can provide white light at high efficiency.